A mebibyte is a unit of data storage that equals 2 to the 20th power, or 1,048,576 bytes.
While a megabyte can be estimated as 10^6 or 1,000,000 bytes, a mebibyte is exactly 1,048,576 bytes. This is to avoid the ambiguity associated with the size of megabytes. A mebibyte is 1,024 kibibytes and precedes the gibibyte unit of measurement.
For a list of other units of measurements, view this Help Center article.